This invention relates to an inspection method and an inspection apparatus for semiconductor circuits with a plurality of semiconductor devices.
In production processes of various semiconductor devices consisting of circuit boards with a plurality of semiconductors mounted thereon, after assembly on a circuit board, the functioning of the semiconductor circuit board (workpiece) is inspected before it is transferred for shipment or movement to the next process. In performing the functional inspection, conventionally, the quality (defective or non-defective) of the workpiece has been determined by applying a working current for the semiconductor devices to the workpiece and a test is performed of whether each semiconductor device works or not.
The previous testing methods and apparatus do not in all instances offer a complete test of each semiconductor in the complete circuit. For example, in a semiconductor circuit with a plurality of semiconductors connected in parallel, if one device is disconnected due to a open breakage, the current flows into the other devices, so that no defect of the workpiece will be detected.
Recognizing this defect in the testing procedure, it has been proposed to apply a large current, over the normal limit value, to flow to detect the existence of a device subject to open breakage. However, if such a large current is inputted to the workpiece for inspection, when a defective device exists, the other normal devices may all be broken. This wastes the workpiece and decreases the yield rate, thus increasing the piece price. Therefore, a one hundred percent inspection is dispensed with and a sampling inspection is performed for each lot. Obviously this results in insufficient reliability of the inspection.
In this case, even if deterioration of the working characteristic of the whole workpiece can be determined, it is impossible to determine which device is defective. On the other hand, if all the devices are inspected individually, a measuring apparatus with multiple minute inspection probes would be required. In such an event, the measuring apparatus would be a complicated one and expensive. Also, if the same loading voltage and current as in the condition of actual use are applied to each workpiece, the power supplying device and the loading device would be expensive.
In addition, if a device develops only a small electrostatic breakdown, it will still allow current to flow and would pass a conventional inspection method. In the case of such an electrostatic breakdown, the device will initially work, but deterioration of the broken-down device progresses during its use, causing malfunction of the whole circuit and decreasing the circuit life.
Therefore it is an object of this invention to provide an inspection method and an inspection apparatus for a semiconductor circuit that is capable of determining reliably the quality (defective or non-defective) of each device in the circuit even if a plurality of semiconductor devices are connected in parallel.
This invention is adapted to be embodied in an inspection method for a semiconductor circuit with a plurality of connected semiconductor devices. The method comprises the steps of applying an electrical load on the circuit, taking a photograph of the circuit with a thermographic camera to detect heat development of each semiconductor device in response to the applied load, and determining the quality of circuit and semiconductor devices based on the heat development.
In a preferred embodiment the temperature of the devices are measured at different points of time, and the quality (defective or non-defective) of the device is determined based on the temperature difference.
A further feature of the invention is adapted to be embodied in an inspection apparatus for a workpiece consisting of a semiconductor circuit with a plurality of connected semiconductor. The inspection apparatus comprises an apparatus body on which a workpiece to be inspected is set. A loading circuit for applying load corresponding to the condition of use to the workpiece is also provided along with a power source for supplying a working current to the workpiece through the loading circuit. A drive waveform generating circuit applies a drive signal to the workpiece. A thermographic camera takes photographs of the workpiece set on the apparatus body and an image processor receives signals from thermographic camera. Finally a control for controls the inspection apparatus to perform an inspection program.